Agents of phaeohyphomycosis (Exophiala, Alternaria, Cladophialophora and other dematiaceous molds)
- Fungus
- For completeness
Dark-pigmented molds from soil and plants. They cause skin cysts after splinters, sinus infections and, rarely, brain abscesses.
Also called: dematiaceous fungi, black fungi, Exophiala, Alternaria, Cladophialophora bantiana, Bipolaris, Curvularia
Quick facts
- Type
- Fungus · Molds and dermatophytes
- Gram / shape
- In tissue
- Spread
- Traumatic implantation of soil
- Causes
- Subcutaneous phaeohyphomycosis
- Treatment
- Surgical excision of cysts and
At a glance
- Shape
- In tissue: brown septate hyphae, yeast-like cells or short chains, never muriform bodies or sulfur granules
- Family
- Many; the black yeasts Exophiala and Cladophialophora belong to Herpotrichiellaceae (Chaetothyriales)
- Type
- Dematiaceous (melanin-pigmented) molds and black yeasts
- Stain
- Brown on H&E or unstained KOH; Fontana-Masson stain confirms melanin
Morphology
- Brown to olive-black colonies on culture; the pigment is melanin in the cell wall.
- In tissue, pigmented septate hyphae and swollen yeast-like cells, sometimes faint and seen only with Fontana-Masson.
- The absence of muriform bodies separates it from chromoblastomycosis; the absence of grains separates it from eumycetoma.
Transmission
- Traumatic implantation of soil or plant material (splinters, thorns) into the skin.
- Inhalation of spores into the sinuses or lungs.
- Spread through the blood to the brain in some species; not person to person.
Reservoir: Soil, wood, decaying plants and household water systems
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Melanin in the cell wall protects against oxidative killing by phagocytes and is the main shared virulence factor.
- Some species are thermotolerant and neurotropic (Cladophialophora bantiana, Exophiala dermatitidis).
- They can invade tissue in people with no obvious immune defect, but disease is more severe in transplant recipients.
Diseases it causes
- Subcutaneous phaeohyphomycosis: a painless cyst or nodule on a limb, often after a splinter. Sporotrichosis and other subcutaneous mycoses →
- Fungal sinusitis by Bipolaris, Curvularia or Alternaria: allergic or, in immunosuppressed hosts, invasive. Fungal sinusitis (invasive and noninvasive) →
- Cerebral phaeohyphomycosis: brain abscess, classically by Cladophialophora bantiana, even in immunocompetent people. Brain abscess →
Clinical picture
- The subcutaneous cyst grows slowly over months and is often mistaken for a ganglion or epidermal cyst.
- Transplant recipients may present long after transplantation with nodules, pneumonia or dissemination.
- Brain abscess presents with headache, focal deficit and seizures; mortality is high.
Diagnosis
- Biopsy or aspirate: brown septate hyphae; Fontana-Masson stain is relatively specific for melanin in tissue.
- Culture on Sabouraud agar grows dark colonies; species are identified by morphology and ribosomal DNA sequencing.
- No routine antigen or serologic test exists; galactomannan and beta-D-glucan are unreliable here.
Treatment
Surgical excision of cysts and, when possible, of brain abscesses is the key step. Triazoles (voriconazole, posaconazole, itraconazole) are the most active drugs; lipid amphotericin B is used in severe disease. There are no interpretive breakpoints, and outcomes in brain infection are poor.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Gloves and closed footwear when working with wood, soil or plants.
- Prompt removal and cleaning of splinters.
- Watching for slow nodules in transplant recipients.
Test yourself
Think of the answer, then tap the question to see it.
What feature defines the agents of phaeohyphomycosis?
Melanin in the cell wall: they appear as brown septate hyphae or yeast-like cells in tissue.
Which stain highlights melanin when the pigment is faint?
Fontana-Masson.
How does phaeohyphomycosis differ from chromoblastomycosis in tissue?
Phaeohyphomycosis shows brown hyphae; chromoblastomycosis shows muriform (sclerotic) bodies.
Which dematiaceous mold is classically linked to brain abscess?
Cladophialophora bantiana, which can infect people without obvious immunosuppression.
Connections
← Back to the group: Molds and dermatophytes
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Phaeohyphomycosis in Transplant Patients (Journal of Fungi (PMC), 2015); U.S. Case Report of Cerebral Phaeohyphomycosis Caused by Ramichloridium obovoideum (R. mackenziei): Criteria for Identification, Therapy, and Review of Other Known Dematiaceous Neurotropic Taxa (Journal of Clinical Microbiology (PMC), 1998).
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Representative model, for educational purposes only.